multifactorial Flashcards
exam 1
distinct variant of a phenotype characteristics that may be inherited
trait
results from the influence of only one gene
monogenic trait
results from the combined influence of multiple genes
polygenic trait
results from the combined influence of multiple genes and environmental factors
multifactorial trait
combined contribution of genes and environmental factors in the causation of a particular disease or trait
multifactorial inheritance
(2) multifactorial traits
(1) Quantitative
(2) threshold
continuous range of measurement, numerical scale, follows a normal or bell-shaped distribution in populations
Quantitative
examples of quantitative traits
height, weight, blood pressure, intelligence
trait is either present or absent
threshold
liability follows a bell-shaped distribution, and those individuals exceeding the threshold on the liability scale will express the trait
threshold
examples of threshold traits
club foot, diabetes, cleft lip and palate, pyloric stenosis
total genetic and environmental factors that contribute to development of a trait
liability
amount of liability required to exhibit the trait
threshold
true or false: liability may be different for males and females
true
m?f for cleft lip and palate
m>f
m?f for congenital hip dysplasia
f>m
m?f for pyloric stenosis
m>f
m?f for autism
m>f
signs of multifactorial inheritance (4)
(1) familial concentration of a disease or trait without a clear mendelian pattern of inheritance
(2) absence of clear biochemical defects resulting from a single abnormal gene
(3) considerable variation in severity and expression of the phenotype
(4) gender difference in the frequency of occurrence
____ ____ are less clear in multifactorial traits than for those that follow mendelian inheritance
recurrence risks
_____ is obtained by observation in family or population studies
data
5 recurrence risk rules
- the greater the severity of the proband, the greater the recurrence risk
- recurrence risk is greater if the proband is of the less commonly affected sex
- recurrence risk is higher if more than one family is affected
- recurrence risk decreases rapidly in more distantly related individuals
- recurrence risk for first degree relatives is approx. the square root of the population incidence of the trait
true or false:
the lesser the severity, the higher the recurrence risk
false–> higher severity, higher risk
is the trait due to genes, environment, or both?
estimate heritability
can we locate the causal genes for this trait?
perform linkage analysis ‘family studies’
can we identify the specific risk alleles for this trait?
perform association studies “ population-based studies”